Since PLAXIS 2D 2015, the user interface provides an option to copy or array objects: first select the items you want to copy (array), and then choose the array tool in Structures mode:
This is also possible using the command line with the arrayr command. For older versions (2D AE), the command line is the only option to perform this operation.
The command has the following structure:
arrayr (Line_1 Point_33) A B C
For a bigger selection of objects it is possible to quickly copy all the names to the command line using this tip and trick on Obtain Object names easily to use in commands